1. Field of the Invention
The present invention relates to a vehicle-behavior control system for a vehicle, including actuators, wheel speed sensors, a controller, a wheel speed sensor, failure detecting means and a fail-safe means. The actuators are capable of changing the vehicle behavior. The wheel speed sensors individually detect a plurality of wheel speeds, respectively. The controller determines whether the control of the vehicle behavior should be carried out, based on the wheel speeds detected by the wheel speed sensors, respectively, and controls the operations of the actuators based on the result of the determination. The wheel speed sensor failure detecting means detects a failure of the wheel speed sensors based on the mutual comparison of the wheel speeds detected by the wheel speed sensors, respectively. The fail-safe means performs a predetermined fail-safe operation based on a detection of failure of the wheel speed sensors by the wheel speed sensor failure detecting means.
2. Description of the Related Arts
A conventionally known vehicle behavior control system (for example, see Japanese Patent Application Laid-open No. 3-202775 and Japanese Utility Model Application Laid-open No. 63-23650) in an anti-lock brake control system in a vehicle, detects an abnormality of one or more of a plurality of wheel speed sensors, due to the sensor falling-off the wheels or the like, by the wheel speed or speeds of the one or more wheels being lower than the other wheel speeds. Thus, a fail-safe operation such as the turning-ON of a warning lamp, the restoration to a normal brake state and the like is carried out.
If a vehicle driver accidentally drives the vehicle with a parking brake set, or applies the parking brake for a side-turn operation during traveling of the vehicle, the wheel speed of the wheel to which the parking brake has been applied is greatly decreased when compared with the wheel speeds of the other wheels. Therefore, in the known system, the failure of the wheel speed sensor can be accidentally detected, so that the fail-safe operation is carried out.
To solve such a problem, detection of the failure by the wheel speed sensor failure detecting means is carried out over a relatively long time. Thus, it is difficult for the fail-safe operation to be produced. Another way to solve this problem is to prohibit the detection of the failure by the wheel speed sensor failure detecting means when the parking brake is set. However, if the time for detection of the failure by the wheel speed sensor failure detecting means is set to a relatively long time, the start of the fail-safe operation is delayed when the wheel speed sensor has actually failed. In addition, if the detection of the failure by the wheel speed sensor failure detecting means is prohibited immediately upon application of the parking brake, it is difficult to detect the failure of the wheel speed sensor when a switch for detecting the operation of the parking brake or the like has failed. If the fail-safe operation is conducted when the application of the parking brake takes a given time or more, the detection of the failure of the wheel speed sensor cannot be made. For example, when the vehicle is traveling with a light parking brake applied to such an extent that an influence is exerted on the antilock brake control, fail-safe processing is carried out, which is not preferable.